This is an open, non-randomized, phase I-II, pilot study, which evaluates the combination of optimum cytoreductive surgery and hyperthermic intraoperative peritoneal chemotherapy (HIPEC) with mitomycin C (MMC) and irinotecan. The latter drug will be administered in escalating doses to patients with gastric, colorectal, appendicular, or primary peritoneal carcinosis (PC).